Method for operating an electrically actuable feed pump in a hydraulic circuit

1. A method for operating an electrically actuable feed pump comprising: an electric motor in a hydraulic circuit, which draws in a normal supply of fluid from a fluid sump, wherein the fluid circulated in the hydraulic circuit can be fed back into the fluid sump, wherein air intake occurs at least partially during a fluid undersupply condition, wherein the electric motor is integrated with a control circuit, which is provided with a control unit, which actuates the electric motor on the basis of an actual rotational speed and of a target rotational speed, wherein the control unit is associated with an evaluation unit for detection of the fluid undersupply condition, which is provided with a filling state model unit, wherein the evaluation unit compares the actual rotational speed of the electric motor to a reference rotational speed at an equivalent current consumption in order to detect the fluid undersupply condition, wherein the equivalent current consumption is correlated with the reference rotational speed, wherein the filling state model unit maintains a predictive model which generates a predicted fluid level of the fluid sump based on input data, the input data of the predictive model comprising a time variable and an occurrence of at least one event which exerts influence on an actual fluid level of the fluid sump, and wherein an evaluation of the feed pump for detection of the fluid undersupply condition is carried out only upon the fulfillment of a test condition in which the predictive model predicts a predicted fluid level of the fluid sump that is above a specified level.

2. The method according to claim 1 , wherein the electric motor of the feed pump is provided with a current limit for overload protection, by which an actual current consumption of the electric motor is limited to a maximum current consumption, wherein a maximum normal supply rotational speed is determined from a rotational speed corresponding to the actual rotational speed of the electric motor which occurs when the electric motor is supplied with the maximum current consumption and the feed pump is provided with a normal fluid supply without the intake of air, and wherein, during a fluid undersupply condition, the target speed is set to be greater than the maximum normal supply rotational speed.

3. The method according to claim 2 , wherein the evaluation unit is provided with a comparison unit which compares the actual rotational speed of the electric motor with the reference speed, wherein the fluid undersupply condition is determined to be present when the actual rotational speed of the electric motor is greater than the reference speed, wherein the actual rotation speed of the motor is that which occurs when the motor is supplied with the maximum current consumption, wherein the reference speed is a correlating maximum normal supply rotational speed.

4. The method according to claim 3 , wherein the comparison unit is associated with a rotational speed constancy unit, by which it is detected whether the electric motor is operated at a constant actual rotational speed, wherein the comparison between the actual rotational speed of the electric motor and the maximum normal supply rotational speed is carried out only if the rotational speed constancy unit determines the electric motor is operated at the constant actual rotation speed.

5. The method according to claim 3 , wherein, after checking for fluid undersupply, the target speed is reset from a testing speed, and the evaluation unit is deactivated.

6. The method according to claim 2 , wherein the maximum normal supply rotational speed is determined empirically by the evaluation unit, and the maximum current consumption and a correlating maximum normal supply rotational speed are stored as a pair of values in the evaluation unit, wherein a plurality of the pair of values are stored, each pair of values being respectively associated with a different operating temperature.

7. The method according to claim 2 , wherein in order to provide the electric motor with the maximum current consumption, a target rotational speed for the electric motor is set by the control circuit to a speed which exceeds an anticipated maximum rotational speed at the maximum current consumption, so that performance deviations of the feed pump from a reference feed pump may be taken into consideration.